Field of the Invention
The present invention relates to an optical coherence tomography microscopy apparatus.
The present invention further relates to an optical coherence tomography microscopy method.
Related Art
EP 1 892 501 discloses an interferometric optical setup that uses a low temporal coherence of a tunable broad-band light source to resolve the axial dimension. The set-up includes a single opto-mechanical or electronic scanning mechanism for accessing different object depths, and a two-dimensional photo sensor device capable of demodulating the temporally or spatially modulated scanning signals to reconstruct the object's full volume.
The cited European patent does not specify how the photo sensor device demodulates the scanning signals. Standard demodulation techniques are known that involve band-pass filtering, rectifying and low-pass filtering the scanning signals. Generally this requires large RC constants, which are not compatible for implementation in CMOS processes.
It is noted that U.S. Pat. No. 6,006,128A discloses a method for generating a velocity-indicating, tomographic image of a sample in an optical coherence tomography system. The method includes a first step of (a) acquiring cross-correlation data from an interferometer. The cross-correlation data is used to generate a grayscale image indicative of a depth-dependent positions of scatterers in the sample. The cross-correlation data is processed to produce a velocity value and location of a moving scatterer in the sample and colors are assigned to the velocity value. The data acquisition system also utilizes a calibration interferometer for providing a calibration of a reference arm position during interferogram acquisition. The system disclosed therein is not intended to scan a surface profile, but serves to measure velocity by means of detecting a frequency shift (the dopplershift) of a reference mirror with respect to the object under surveillance. This necessitates split light paths.
It is further noted that US2009/268213A1 discloses an apparatus for measuring the axial length of a human eye. The apparatus comprises a low coherence light source; a beam splitter; a fast displacement module for rapidly varying the path length within a reference arm of an interferometer. The apparatus further includes a laser directing a laser beam that is co-propagating with light from the low coherence light source into the displacement module. Paragraph [0034] states that “the computer 124 receives a signal from interferometer 134, which enables monitoring of the changes of the path length of reference arm 120 with a sub-micrometer precision. US2009/268213A1 does not disclose how this signal is used by the computer. However, in the same paragraph [0034] it specifies that: “The wavelength of the laser should be different from the spectrum of the low coherence light source 112.”
It is still further noted that US2010/309479A1 discloses an interference measuring device that comprises a displacement detecting unit, a piezoelectric actuator and a drive unit, a mirror, a stage, a drive unit, and a control unit. According to a result of optical path length difference detection by the displacement detecting unit the control unit controls optical path length difference adjusting operations by the piezoelectric actuator to sequentially set the optical path length difference to one of a plurality of target values.
It is still further noted that U.S. Pat. No. 5,659,392A discloses an associated dual interferometric measurement apparatus for determining a physical property of an object, such as thickness, group index of refraction, and distance to a surface. The apparatus includes a non-coherent light interferometer and a coherent light interferometer in association so as to share a variable optical path delay element. Thickness measurements can be made, for example, of solids, liquids, liquids moving along a horizontal plane, or liquids flowing down a plane. Thickness measurements of multiple layers can be made. The analog output of photodetector indicative for the low-coherence radiation interference pattern is amplified and filtered by an electronic module, and digitized by utilizing the coherent light interferometer data acquisition trigger pulses by processing electronics that is capacitively coupled to a further photodetector.
Known optical coherence tomography microscopy apparatuses are typically intended for use in well-controlled circumstances, such as in a laboratory environment, but are unsuitable for general application where vibrations in the environment and other disturbances cannot be avoided. Accordingly, another approach is desired that is more generally applicable in such environments.